Such sensors usually include at least one curved measuring tube for guiding the fluid and at least one housing surrounding the measuring tube. The measuring tube vibrates during operation.
The main representatives of such sensors are mass-flow/density/viscosity sensors operating on the Coriolis principle. These sensors can not only be used to measure the instantaneous mass flow of the fluid flowing in the pipeline, but also the density of the fluid, on the basis of the instantaneous oscillation frequency of the measuring tubes, and the viscosity of the fluid, on the basis of the power required to maintain their oscillations, as well as the temperature of the fluid. The mass flow is, by definition, the mass of fluid flowing through each measuring tube cross section per unit time.
U.S. Pat. No. 4,876,898 describes a Coriolis mass flow sensor for use at temperatures up to 220° C. This sensor, which is suitable for use in a pipeline at least temporarily containing fluid flowing therethrough, includes:    two parallel, curved measuring tubes that vibrate during operation and guide the fluid,    a metal housing covering the measuring tubes, and    a supporting arrangement of metal,            in which the measuring tubes are held at their inlet and outlet ends in a manner such that the tubes can oscillate, and        out of which the measuring tubes protrude sideways,        which metal housing includes a first cap half and a second cap half for enclosing the measuring tubes,                    an edge of which first cap half includes a circular-arc-shaped first edge portion lying in a first plane and having a first radius of curvature and a circular-arc-shaped second edge portion lying in a second plane perpendicular to the first plane and having a second, significantly smaller, radius of curvature, and            an edge of which second cap half includes a circular-arc-shaped third edge portion lying in a third plane and having the first radius of curvature and a circular-arc-shaped fourth edge portion lying in a fourth plane perpendicular to the third plane and having the second radius of curvature,            wherein the first and second edge portions are welded continuously to one another, and            wherein the second and the fourth edge portions are welded continuously to the supporting arrangement.                        
Additionally, U.S. Pat. No. 5,301,557 describes a Coriolis mass flow sensor, which is suitable for use in a pipeline at least temporarily containing fluid flowing therethrough and which includes:    two parallel, curved measuring tubes that vibrate during operation and guide the fluid,    a supporting arrangement of metal,            in which the measuring tubes are held at their inlet and outlet ends in a manner such that the tubes can oscillate, and        out of which the measuring tubes protrude sideways, and            a curved metal tube completely enclosing the measuring tubes,            which follows the route of the measuring tubes, while maintaining a uniform spacing therefrom, and        which, after having been bent to match the route of the measuring tubes and then temporarily divided into two equal tube halves along a longitudinal cutting plane, is then assembled to enclose the measuring tubes and put back together again by welding of the tube halves to one another, and        whose ends are welded continuously with the supporting arrangement.        
The mentioned U.S. Pat. No. 5,301,557 also describes a Coriolis mass flow sensor, which is suitable for use in a pipeline at least temporarily containing fluid flowing therethrough and which includes:    two parallel, curved measuring tubes that vibrate during operation and guide the fluid,    a supporting arrangement of metal,            in which the measuring tubes are held at their inlet and outlet ends in a manner such that the tubes can oscillate, and        out of which the measuring tubes protrude sideways, and            a metal tube completely enclosing the measuring tubes and composed of sectionally straight tube portions terminally welded to one another,            which are made from deep-drawn half-shells continuously welded to one another following their placement around the measuring tubes.        
Finally, a Coriolis mass-flow/density sensor is offered by the Endress+Hauser group of firms under the label Promass F. This sensor, which is suitable for use in a pipeline at least temporarily containing fluid flowing therethrough, includes:    two parallel, curved measuring tubes that vibrate during operation and guide the fluid,    a metal housing enclosing the measuring tubes,            having a supporting tube of metal,                    in which the measuring tubes are held on their inlet and outlet ends in a manner such that the tubes can oscillate, and            out of which measuring tube segments protrude sideways through two cutouts, and                        having a deep-drawn metal cap for covering the measuring tube segments,                    an edge of which is continuously welded with the supporting tube.                        
The deep drawing of shaped bodies of metal, including also the above-mentioned metal caps, is done in a corresponding metal deep-drawing die, the manufacturing costs of which are very high. Deep drawing is, consequently, worthwhile only in the case of sufficiently high production quantities of the shaped bodies to be produced therewith. Since the mentioned Coriolis mass-flow/density sensor Promass F is manufactured in a number of different standard, nominal sizes up to 100 mm, in each case in large production quantities, deep drawing of the metal caps is economical, even though a separate deep drawing die is required for each nominal size.
However, if, for certain nominal sizes, especially for nominal sizes greater than 100 mm, but even for non-standard nominal sizes less than 100 mm, only smaller production quantities are expected, then the manufacture of the metal caps by means of such deep drawing dies specially sized for the individual nominal sizes cannot be practically realized, because of the high costs.